1. Field of the Invention
The present invention relates generally to jaw assemblies and related jaw components for a jaw chuck for holding a workpiece to a spindle of a machine.
2. Background Information
Jaw assemblies are used for holding a work piece to the spindle of a rotary machine, such as a lathe. A jaw assembly typically works in conjunction with additional jaw assemblies coupled to a chuck body for simultaneously reciprocating radial movement with respect to the chuck body to provide self-centering gripping of the workpiece. A chuck jaw assembly typically includes a radially displaceable master jaw mounted on the chuck body and a top jaw releasably secured to the master jaw to facilitate rapid jaw change. The top jaw provides a gripping or clamping surface adapted to engage a work item at either its inside or outside diameter. The top jaw holds the item during a machining operation. Typically the clamping surfaces on the top jaw are machined after the top jaws have been mounted on the master jaws to assure concentricity of the clamping surfaces relative to the axis of rotation of the chuck.
Jaw assemblies of the rapid change variety are particularly useful for repetitive small batch production operations involving frequent changeover. At the end of a production run the top jaws are usually removed from the chuck and replaced with another set of top jaws adapted to accommodate the next workpiece which may vary substantially with respect to the previously machined workpiece. Precise concentricity of the jaw clamping surfaces must be maintained to achieve close tolerance workholding. Desired close tolerances can be maintained by rematching the top jaws after changeover, however the rematching process is costly and time consuming.
The top jaws and master jaws may also be marked and maintained as matched pairs for subsequent use in order to maintain precise concentricity after jaw changeover. This approach, which is recommended with all jaws, including the present ones, is subject to error and makes the interchangeability of top jaws difficult or impossible. If proper matching is not maintained, desired surface concentricity may be lost, resulting in poor performance or damage to workpieces or machinery.
Various jaw assemblies have been available which provide interchangability among top jaws so that the jaws may be randomly assembled with the master jaws on a chuck without rematchining while still maintaining concentricity. One example of such a jaw assembly that provides a sustained biasing force of substantial magnitude for urging reference surfaces on the jaws into and maintaining the surfaces in coengagement to assure precise top jaw and master jaw alignment is found in U.S. Pat. No. 5,842,705 to Tabachenko et al. However, despite their ingenuity, this and other references generally use complex mounting mechanisms and are usually costly to produce. Such interchangeable jaw assemblies often use spring biasing or other complicated mechanisms for urging surfaces on the master and top jaws into coengagement and often fail to provide the degree of reliability and chucking concentricity desired.
Prior jaw assembly devices typically include a top jaw mounted rigidly to a master jaw or chuck. Once the top jaw is rigidly mounted, then the chuck is operated to close the jaw or respective jaws upon a piece to be machined. The rigid jaw mounting generally requires the set of jaw assemblies to be in proper alignment with respect to each other. Even slight differences or changes in the top jaw at a workpiece contact point may cause the structure to be out of balance. Obtaining precise concentricity is difficult due to the rigid mounting of the respective jaw assemblies. It would be desired to establish a structure where it would be possible to have the top jaw self-adjust when pressure is applied to the respective jaws while tightening the jaws about a workpiece. A self-adjusting top jaw could thereby act as an automatic setting or centering of the jaw elements to obtaining a concentric arrangement. Of course, having the jaws set into a secure position after tightening is desired so proper use of the device, such as a lathe chuck, may occur without failure or damage to the equipment, surroundings, or workpieces.
Heretofore there has been little, if any, appreciation that a soft, loose or non-rigid initial mounting of a jaw, which when tightened by a normal chuck tightening operation, could possibly result in the setting of the jaw into a secure or rigid concentric mount. Such function would be contrary to the typical practice of rigidly presetting the jaw, and instead would utilize the resulting tightening forces to accomplish the concentric mounting.
Accordingly, it is a general desire of the present invention to provide an improved interchangeable type quick-change jaw assembly of simple construction where a top jaw and master jaw are configured so as to flex and self-adjust into proper concentric alignment. A further desire is to provide such a jaw assembly of simple construction where a single fastener releasably secures a top jaw to a master jaw and where the jaws are configured so as to provide a secure engagement and precise top jaw and master jaw alignment. These and other desires may be apparent as presented throughout the remainder of this specification.